Q.22 The ideal value for the backbone dihedral angles for antiparallel
β-sheets are:
- (A) φ = −120° and ψ = +125°
- (B) φ = −139° and ψ = +135°
- (C) φ = −120° and ψ = +130°
- (D) φ = −115° and ψ = +140°
Choose the correct answer from the options given below:
- (A) and (D) only
- (B) only
- (A), (B) and (C) only
-
Ideal Backbone Dihedral Angles for Antiparallel β-Sheets: MCQ Answer and Explanation
The ideal dihedral angles for antiparallel β-sheets center around φ ≈ -139° to -140° and ψ ≈ +135°, making option (B) the precise match. This configuration maximizes hydrogen bond stability in antiparallel strands.
Correct Answer
(B) only
Option Analysis
-
(A) φ = −120° and ψ = +125°: These approximate parallel β-sheet values (φ ≈ -120°, ψ ≈ +115°-125°), not antiparallel.
-
(B) φ = −139° and ψ = +135°: Matches standard antiparallel β-sheet angles (φ ≈ -140°, ψ ≈ 135°).
-
(C) φ = −120° and ψ = +130°: φ is too shallow for antiparallel; ψ is close but inconsistent.
-
(D) φ = −115° and ψ = +140°: φ deviates significantly from the ideal -139°/-140° range.
| Option |
φ Value |
ψ Value |
Matches Antiparallel β-Sheet? |
| (A) |
-120° |
+125° |
No (parallel-like) |
| (B) |
-139° |
+135° |
Yes |
| (C) |
-120° |
+130° |
No |
| (D) |
-115° |
+140° |
No |
